1. Field of the Invention
The present invention relates to a chucking device for making a disc having a disc shape freely attachable and detachable and a brushless motor and a disc driving device in which the chucking device is installed.
2. Description of the Related Art
In recent years, development of DVD having large capacity as a next-generation DVD (Digital Versatile Disc) for recording a high-quality image demanding a large capacity has been aggressively promoted. In the high-capacity DVD, the high capacity is realized in such a manner that a track pitch is changed from 0.64 μm which was conventionally adopted to 0.32 μm which is a half of the conventional length, and a blue-violet laser having a short wavelength is correspondingly used as a laser for recording and reproduction in place of a red laser having a long wavelength which was conventionally used so that a recording density is increased. Further, the high-capacity DVD is rotated at such a high speed as 10,000 rotations per minute so that a recording speed is increased and a high double speed is realized in the DVD.
In order to retain the recording disc such as the high-capacity DVD, a brushless motor provided with a chucking device for retaining an inner peripheral edge of a central through hole of the recording disc using a plurality of retaining parts having a claw shape or the like and energized by a spring was conventionally adopted.
However, in the chucking device for retaining the recording disc using the plurality of claws, in which only the retaining parts having the claw shape or the like and radially protruded are used to retain the inner peripheral edge of the central through hole of the recoding disc, each retaining part has a different retaining force for retaining the inner peripheral edge of the central through hole of the recording disc. As a result, an aligning accuracy of the recording disc is deteriorated when the recording disc is rotated at such a high speed as 10,000 rotations per minute or in the case where a balancing performance of the recording disc is remarkably inferior. Due to the disadvantage, the high-capacity DVD as the next-generation DVD possibly included the disadvantage that an error occurred in recording and reproduction.
In addition to the foregoing disadvantage, in the chucking device, in the case where the recording disc loses even a slight balance when rotated at such a high speed as 10,000 rotations per minute, the retaining parts and the inner peripheral edge of the central through hole of the recording disc strongly abut each other in one direction by a centrifugal force. This makes positions at which the retaining parts and the recording disc abut each other shifted, which also shifts a position of the recording disc. As a result, a recording/reproducing position changes in an initial stage of the rotation and during the rotation, which possibly caused an error in the recoding and reproduction. The worst possible incident was that the recording disc was possibly disengaged from the chucking device. Further, such a phenomenon that the recording disc and the retaining parts unfavorably bite into each other and move together is generated under the influence of the centrifugal force. When the biting phenomenon is generated, a force which returns a cone part to its original position is enhanced by a reaction generated from the phenomenon, and the recording disc is rapidly returned to its original retaining position at a moment when the force becomes stronger than the force in the meshing direction. As a result, the drastic position shift of the recording disc makes it impossible for a reading function of the recording disc to follow the position shift of the recording disc, which may cause an error in the recording and reproduction. Further, if the retaining force of the recording disc is weak, a vibration is generated between the recoding disc and the chucking device when the recording disc is rotated at a high speed. The vibration makes the recording disc rotate while moving the disc by a minute distance, which also possibly caused an error in the recording and reproduction.